OPIOIDS AND STRESS: THE PAG

该应用建议使用解剖学和电生理学相结合的方法来了解阿片样物质如何调节腹外侧导水管周围灰质（PAG）的神经元活动，并进一步了解PAG-阿片样物质系统内的可塑性机制。申请人是一名经验丰富的超微结构神经解剖学家，将在该支持机制下接受电生理技术和应激神经生物学的培训。PAG具有多种行为功能，但最典型的特征是吗啡产生和应激诱导的镇痛。阿片被认为通过抑制局部gaba能中间神经元并随后解除对PAG输出的抑制而作用于PAG，然而，一些解剖学观察表明，阿片可能通过其他机制起作用。最引人注目的是，mu阿片受体（MOR）存在于一个大的亚群中（约为1000个）。40%)腹侧PAG的髓质突起神经元。在这里，我们假设MOR可能对gaba能与非gaba能的PAG神经元有不同的作用。这一假设将通过使用细胞内记录技术确定MOR激动剂对PAG细胞的影响来验证。研究的细胞将充满神经生物素，并免疫组织化学标记GABA。某些应激模式，例如长时间暴露于间歇性和不可避免的休克（IS），对阿片系统有长期持久的影响。具体来说，暴露于IS 24小时后会增强低剂量吗啡的镇痛作用。PAG既参与对应激源的急性反应，也参与吗啡和应激性镇痛。这表明PAG中MOR和/或δ阿片受体（DOR）功能的变化可能参与IS引起的吗啡镇痛效力的变化。在具体目标2和3中，解剖学和电生理学方法将协同使用，以确定与该现象相关的MOR和DOR功能的变化。这些研究将揭示吗啡镇痛作用背后的细胞机制。此外，了解压力对阿片类药物系统的影响尤为重要，因为压力被认为是导致成瘾和药物寻求行为复发的主要因素。

This application proposes using combined anatomical and electrophysiological means to understand how opioids function to modulate neuronal activity in the ventrolateral periaqueductal gray (PAG) and furthermore to understand mechanisms of plasticity within the PAG-opioid system. The applicant is an experienced ultrastructural neuroanatomist and will be trained under this support mechanism in electrophysiological techniques, as well as in stress neurobiology. The PAG subserves several behavioral functions but has been most well characterized as a site of morphine-produced and stress-induced analgesia. Mu opioids are thought to act in the PAG by inhibiting local GABAergic interneurons and subsequently disinhibiting PAG output, however, several anatomical observations suggest the mu opioids may act through additional mechanisms. Most strikingly, mu opioid receptor (MOR) is present on a large subpopulation (approx. 40%) of medullary projecting neurons in the ventrolateral PAG. Here we hypothesize the MOR may function distinctly on GABAergic vs. nonGABAergic PAG neurons. This hypothesis will be tested by determining the effects of MOR agonists on PAG cells using intracellular recording techniques. Studied cells will be filled with neurobiotin and immunohistochemically labeled for GABA. Certain stress paradigms, for example a prolonged exposure to intermittent and inescapable shock (IS) have long lasting effects on the opioid system. Specifically, exposure to IS potentates the analgesic effects of low doses of morphine 24 hours later. The PAG is involved in both the acute response to stressors, and morphine and stress induced analgesia. This suggests the hypothesis that changes in MOR and/or delta opioid receptor (DOR) functioning in the PAG may participate in IS produced changes in morphine's analgesic potency. In Specific Aims 2 and 3, anatomical and electrophysiological methods will be used in concert to determine the changes in MOR and DOR function relating to this phenomenon. These studies will shed insight into the cellular mechanisms that underlie morphine's analgesic effects. Furthermore, understanding stress effects on the opioid system are particularly important since stress has been implicated as a major factor contributing to addiction and relapse to drug seeking behavior.